1. Field of the Invention
The present invention relates to a circuit breaker to be used in an electric power system.
2. Description of the Prior Art
A convention circuit breaker which is a doublebreak type gas-insulated circuit breaker with closing resistors is described referring to FIGS. 16 to 21.
FIG. 16 is a sectional side view showing a constitution of the conventional circuit breaker in a closed state. In FIG. 16, elements which are positioned in left-hand in the figure are further sectioned and elements in right-band are not sectioned. The elements in left band and the elements in right band are substantially the same and positioned substantially symmetrical.
In FIG. 16, an insulation gas such as SF.sub.6 102 is filled in a main tank 101. Two main contacts 200 are symmetrically positioned with respect to the center of the main tank 101 and they are supported by a frame conductor 301. The frame conductor 301 is supported by an insulation holder 302 in a center branch drum port of the main tank 101. The main contacts 200 and the frame conductor 301 are positioned on a center axis of the main tank 101. The main contacts 200 respectively consist of a stationary electrode 201 and a moving electrode 202.
FIG. 17 is a sectional side view showing a detail constitution of a switching part of the conventional circuit breaker. As shown in FIG. 17, the stationary electrode 201 and the moving electrode 202 are held by an insulation holder 203. Conductors 204 of the stationary electrodes 201 serve as cooling drums for cooling hot insulation gas in a breaking operation of the circuit breaker. In rear parts of the conductors 204, exhaust openings 204a are formed for exhausting the hot insulation gas therethrough. Connection parts 105 are respectively provided on the conductors 204 to be connected to connection conductors 104 which are respectively held by insulation spacers 103 at the both ends of the main tank 101.
As shown in FIGS. 16 and 17, the insulation tubes 203 respectively have a cylindrical shape. Capacitors 106 are provided on outer peripheries of the insulation tubes 203, and they are electrically connected in parallel with the main contacts 200 in a manner to share voltages of the main contacts 200 evenly. On outer peripheries of the conductors 204, two sets of plural resistors 500 are provided for restraining the surge when the circuit is closed. Resistor contacts 400 are respectively connected in series with respective sets of the resistors 500. The resistor contacts 400 are respectively provided on the outer peripheries of the insulation tubes 203 and obliquely below the main contacts 200. Furthermore, series connections of the resistor contact 400 and the resistors 500 are electrically connected in parallel with the main contacts 200. The moving electrodes 202 of the main contacts 200 and moving resistor contacts 409 of the resistor contacts 400 are respectively coupled with an insulation operation rod 303 via a link mechanism 300 which is provided in the frame conductor 301. The link mechanism 300 is connected to a hydraulic operation apparatus 700 in an operation housing 107 via another link mechanism 600 which is provided in the air.
Constitutions of the above-mentioned individual elements are described in detail. FIG. 17 shows a breaking state of the conventional circuit breaker. In FIG. 17, each of the stationary electrode 201 of the main contact 200 constitutes essentially of a main stationary contact 205, a stationary arc contact 206, a shield 207 and the conductor 204. The main moving electrode 202, which is positioned opposing to the stationary electrode 201, constitutes essentially of a main moving contact 208, a moving arc contact 209, a nozzle 210, a puffer cylinder 211, a piston 213 and a finger contact 214. A piston rod 212 of the piston 213 is slidably held on the frame contact in a manner to make the finger contact 214 serve as a guide. A stationary resistor contact 401 is positioned obliquely below the stationary electrode 201, slidably held on a resistor contact case 402. The resistor contact case is fixed on the shield 207 via an insulation base 403.
As shown in FIG. 17, each piston rod 212 is linked to a main lever 305 via a link 304. Each of the main lever 305 is rotatably held on the frame conductor 301. The insulation rod 303 is coupled to both (right and left sides in the figure) of the main levers 305 via other links 306. Each of the moving resistor contact 409 is linked to an end 308a of a lever 308 via a link 307. Each of the lever 308 is rotatably borne at substantially the center thereof by a pin 309. The pin 309 is provided at substantially the center between a rotation center of the main lever 305 and a coupling part of the link 304 and the main lever 305. The other end of the lever 308 is rotatably borne on a link 310. The link 310 is rotatably borne on the frame conductor 301. In such a link mechanism, the motion of the link part of the link 307 and the lever 308 due to the rotation of the main lever 305 can be considered as a linear motion, and thereby any transverse force does not occur in the moving resistor contact 409.
An upper end 303a of the insulation rod 303 is guided by a guide 311 which is provided on the frame conductor 301, and a lower end 303b of the insulation rod 303 is fixed on a shaft 601. The insulation rod 303 is positioned at the center of the insulation holder 302. The shaft 601 penetrates the center of the bottom face 302a of the insulation holder 302. A shaft real 602 is provided between the shaft 601 and the insulation holder 302 for guiding the sliding motion of the shaft 601 and for maintaining the seal of the SF.sub.6 gas 102 in the main tank 101. An end 601a of the shaft 601 in the air is coupled to a hydraulic piston 701 of the hydraulic operation apparatus 700 via a link mechanism which is constituted by a link 603, a conversion lever 604 for perpendicularly converting the moving direction and a rod end 605.
The hydraulic operation apparatus 700 further comprises an accumulator for charging the oil and a oil pump unit (not shown in the figure) for increasing the pressure of the oil.
FIG. 18 shows a detail constitution of the resistor contact 400 in a breaking state of the circuit breaker. In FIG. 18, a restoration spring 404 is provided in an inner space of the resistor contact 401. An end 404a of the restoration spring 404 contacts an inside face 401a of the resistor contact 401 and the other end 404b of the restoration spring 404 contacts a piston 405 which is fixed on the resistor contact case 402. In the breaking state, the resistor contact 401 is pushed out by a pressing force of the restoration spring 404 since the resistor contact case 402 serves as a stopper. Orifices 406 are provided on the piston 405 for serving as a damper when the stationary resistor contact 401 slides. On the outer surface of the stationary resistor contact 401, a contact piece 407 is provided for electrically connecting the stationary resistor contact 401 to the resistor contact case 402. On an extension of the center axis of the stationary resistor contact 401, resistor elements 501 are provided via an adapter 408 in a manner to be connected electrically in series to the stationary resistor contact 401. The moving resistor contact 409 is positioned opposing to the stationary resistor contact 401, movably held by the frame conductor 301 and electrically connected to the frame conductor 301 by a contact piece 410.
FIG. 19 shows an installation of the resistors 500. For restoring the surge which occurs in the closing operation of the circuit breaker, the resistor contact 400, which is provided in parallel with the main contact 200, is closed prior to the closing of the main contact 200. And thereby, the resistors 500 which are provided in series with the resistor contact 400 are electrically connected. Generally, each of the resistor 500 consists of series connection of many resistor elements 501, thereby a necessary value of the resistor 500 or the series connection of the resistors 500 is/are given by the series connection of the resistor elements 501. And the heat load of the resistor 500 is partially shared by the resistor elements 501. Each of the resistor element 501 has a disk shape and is held by an insulation bar 502 which penetrates the center hole of the resistor element 501. An end 502a of the insulation bar 502 is fixed on an adapter 408 and the other end 502b is fixed on a conductor 503 which is used for connecting another resistor 500'. Another adapter 504 is provided to electrically contact with the left side of the series connection of the resistor elements 501 in the figure. A coil spring 505 is provided between the conductor 503 and the adapter 504 for supplying a pressure to the resistor elements 501. The conductor 503 is shielded by a shield 506 which is used for weakening the electric field. Similarly, the next resistors 500' and 500" are electrically connected in series to each other and held by an insulation base 507 on a shield 207. The other end 510 of the series connection of the resistors 500' and 500" is electrically connected to a conductor 204, thereby the main contact 200 is electrically in parallel to the series connection of the resistors 500, 500' and 500".
The motion of the conventional circuit breaker is described. The closing motion shown in FIG. 17 is executed as follows. By receiving a closing command (from a control apparatus not shown in the figure), the piston 701 of the hydraulic operation apparatus 700 and the rod end 605 start to move in left-hand in FIG. 17. Thereby, the lever 604 rotates in counterclockwise direction, and the shaft 601 moves upward via the link 603. The elements which are positioned in right- and left-hands in FIG. 17 move symmetrically, so that the explanation of the motion is mainly referring to the left-hand ones.
When the shaft 601 moves upward, the insulation operation rod 303 also moves upward. The main lever 305, which is coupled to the insulation operation rod 303 via the link 306, rotates in counterclockwise direction. As a result, the puffer cylinder 211 of the main contact 200 is moved in left-hand via the link 304 and the piston rod 212.
On the other hand, the lever 308, which is linked to the main lever 305 by the pin 309, rotates in clockwise direction around the coupling point 308b to the link 310 by the rotation in counterclockwise direction of the main lever 305. The moving resistor contact 409 moves in left-hand to approach the stationary resistor contact 401 via the link 307. At first, the moving resistor contact 409 contacts the stationary resistor contact 401, and thereby, the resistor contact 400 enters a closing state. At this time, the moving resistor contact 409 pushes the stationary resistor contact 401, and the restoration spring 404 is compressed by pushing of the stationary resistor contact 401 to the resistor contact case 402. Next, the moving arc contact 209 contacts the stationary arc contact 206. Furthermore, the main moving contact 208 contacts the main stationary contact 205. Thereby, the main contact 200 is closed.
The stationary resistor contact 401 is constituted to be able to move with the motion of the moving resistor contact 409. When the stationary resistor contact 401 is pressed by the moving resistor contact 409, the insulation gas of SF.sub.6 in a space formed between the piston 405 and the stationary resistor contact 401 is compressed. When the compressed insulation gas 102 is exhausted from the orifice 406, the resistance serves as a damping force. When the piston 701 reaches to a closing position, the closing motion of the circuit breaker is completed. The closing state of the conventional circuit breaker is shown in FIG. 20.
Next, the breaking motion of the conventional circuit breaker is described. From the closed state of the conventional circuit breaker shown in FIG. 20, when a breaking command is issued from the control apparatus (not shown in the figure), the piston 701 of the hydraulic operation apparatus 700 and the rod end 605 start to move in right-hand in FIG. 17. The lever 604 rotates in clockwise direction and the shaft 601 moves downward via the link 603.
When the shaft 601 moves downward, the insulation operation rod 303 also moves downward. The main lever 305, which is linked to the insulation operation rod 303 via the link 306, rotates in clockwise direction. And the puffer cylinder 211 of the main contact 200 moves to the frame conductor 301 which is positioned in the center of the main tank 101 via the link 304 and the piston rod 212.
On the other hand, the lever 308, which is linked to the main lever 305 by the pin 309, rotates in counterclockwise direction around the coupling point 308b to the link 310 by following to the rotation of the main lever 305 in clockwise direction. The moving resistor contact 409 also moves to the frame contact 301 via the link 307. The stationary resistor contact 401 moves in right-hand by the pressure of the restoration spring 404 following to the movement of the moving resistor contact 409 in right-hand. However, the moving speed of the stationary resistor contact 401 is slower than that of the moving resistor contact 401, since the charged energy of the restoration spring 404 is small and the orifice formed on the piston 405 serves as a damper. Therefore, the resistor contact 400 becomes breaking state soon. After that, the main moving contact 208 of the main contact departs from the main stationary contact 205. The moving arc contact 209 also departs from the stationary arc contact 206, and an arc occurs between them. A state on the way of the breaking operation of the conventional circuit breaker is shown in FIG. 21.
The compressed insulation gas 102 by the piston 213 and the puffer cylinder 211 blows the arc, and thereby, the current flowing in the circuit breaker is cut. Most of the insulation gas heated by the arc passes through the conductor 204. The insulation gas 102 is cooled by the conductor 204 and exhausted from the opening 204a. When the piston 701 reaches to the breaking position, the breaking operation of the conventional circuit breaker is completed. The breaking state of the conventional circuit breaker is shown in FIG. 16.
When the voltage of the electric power system becomes higher and the conventional circuit breaker is used, for example, in 1000 kv system, it is necessary to restrain an overvoltage not only in the closing operation but also in the breaking operation of the circuit breaker for making a transmission-transformation system and/or transmission lines economical. In the conventional circuit breaker configured above, the resistor contact 400 is broken prior to the breaking of the main contact 200. Therefore, the overvoltage in the breaking operation can not be restrained. For restraining the overvoltage that occurs in the breaking operation, a resistor-breaking type circuit breaker, which inserts a resistor contact after breaking the main contact and breaking the resistor contact after a predetermined time period, is necessary. For such the time period of the insertion time of the resistor contact, a time of about 25 ms is necessary according to a computer simulation of the model system. The time period of 25 ms in the breaking operation is longer than that of 10 ms in the closing operation.
On the other hand, the circuit breaker is generally demanded to operate faster in the breaking operation than in the closing operation for obtaining a high circuit breaking performance. For satisfying such a condition, it is necessary that the resistor contact is opened in the vicinity of the final step of the breaking operation after the main contact is opened. Therefore, another special driving apparatus and a delay operation mechanism are demanded to constitute the high-voltage type circuit breaker.
In the above-mentioned demanded high-voltage type circuit breaker, the resistor is inserted not only in the closing operation but also in the breaking operation, so that the heat generated in the resistor becomes larger. For sharing the increased heat by respective resistor elements which constitute the resistor, the number of the resistor elements must be increased and the arrangement of the resistor elements becomes complex. Furthermore, if the resistor is supported by the frame conductor which is positioned at the center of the main tank, mechanical strength of the frame conductor and the other insulation holders and so on with respect to vibration become a problem.
Still more, for responding to the high voltage, the moving speed of the main contact and the resistor contact in the breaking operation must be increased in view of the dielectric strength after the current is cut. Therefore, a high power actuator is necessary to satisfy the moving speed of the main contact and the resistor contact, and each element constituting the circuit breaker must have a sufficient mechanical strength for fitting the high power actuator.